We develop a novel formalism to calculate the optical forces and torques on complex and realistic nanostructures by combining the surface integral equation (SIE) technique with Maxwell's stress tensor. The optical force is calculated directly on the scatterer surface from the currents obtained from the SIE, which does not require an additional surface to evaluate Maxwell's stress tensor; this is especially useful for intricate geometries such as plasmonic antennas. SIE enables direct evaluation of forces from the surface currents very efficiently and accurately for complex systems. As a proof of concept, we establish the accuracy of the model by comparing the results with the calculations from the Mie theory. The flexibility of the method is demonstrated by simulating a realistic plasmonic system with intricate geometry. (C) 2014 Optical Society of America